1. Field of the Invention
The present invention is directed to an x-ray diagnostics installation of the type having a luminescent storage or persistent screen in which a latent x-ray image is stored, means for reading-out the storage screen by exciting the storage screen to luminesce, and an imaging system and a light detector for generating signals corresponding to the image for visual display on a monitor.
2. Description of the Prior Art
An x-ray diagnostics installation is disclosed in German OS No. 24 51 978 wherein a luminescent screen consisting of one or more thermoluminescent storage or persistent luminophores is irradiated with x-rays. The screen functions as a radiation-sensitive transducer, so that electrons are generated, which are stored in voltage traps or wells having a high energy boundary. A read-out means scans the storage screen by picture elements using an additional radiation source, such as a laser, so that the electrons stored in the traps are excited, and can fall back to lower energy levels. The energy difference is emitted in the form of light quanta. The latent x-ray image stored in the screen is read-out in this manner.
During the scanning of a line of the storage screen by a laser beam, the emitted light is acquired by an optical collector, and is imaged onto a light-sensitive entry face of a detector. The output signal of the detector is supplied to a conventional video chain for visual reproduction of the x-ray image.
In order to achieve a fast image read-out, however, the luminophore must also contain a high concentration of traps in which the electrons are not retained, but are spontaneously converted into visible light (spontaneous emission). These traps needed for the read-out event are also occupied with electrons during the x-ray irradiation, and are immediately emptied. This means, however, that a part of the energy of the x-rays is lost during the x-ray exposure, so that only a slight yield of the input energy is obtained.
German OS No. 29 40 454 discloses a method for recording a radiation image on a recording material wherein the spontaneously emitted light of a storage luminophore is acquired by a detector, and is supplied to the x-ray source as a measured value, so that the exposure duration and the level of exposure of the storage luminophore can be controlled thereby. The spontaneously emitted light is thus used only for measurement and control. For the actual image pick-up and image acquisition, again only the relatively slight component of the stored energy is utilized.